<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <table border="1" style="border-collapse: collapse" width="350">
    <thead>
      <tr>
        <th colspan="12">1</th>
        <th rowspan="12">2</th>
      </tr>
      <tr>
        <th rowspan="12">4</th>
        <th colspan="10">5</th>
        <th rowspan="10">6</th>
      </tr>
      <tr>
        <th rowspan="10">8</th>
        <th colspan="8">9</th>
        <th rowspan="8">10</th>
      </tr>
      <tr>
        <th rowspan="8">12</th>
        <th colspan="6">13</th>
        <th rowspan="6">14</th>
      </tr>
      <tr>
        <th rowspan="6">16</th>
        <th colspan="4">17</th>
        <th rowspan="4">18</th>
      </tr>
      <tr>
        <th rowspan="4">20</th>
        <th colspan="2">21</th>
        <th rowspan="2">22</th>
      </tr>
      <tr>
        <th rowspan="2">24</th>
        <th >25</th>
      </tr>
      <tr>
        <th colspan="2">23</th>
      </tr>
      <tr>
        <th colspan="4">19</th>
      </tr>
      <tr>
        <th colspan="6">15</th>
      </tr>
      <tr>
        <th colspan="8">11</th>
      </tr>
      <tr>
        <th colspan="10">7</th>
      </tr>
      <tr>
        <th colspan="12">3</th>
      </tr>
    </thead>
  </table>
</body>
</html>